A SVN-client may be useful if you want to participate in the CHDK development or if you want to keep your own version always up-to-date (see here).

Procedure

The procedure itself is pretty straightforward: Try to figure out what the source code does, apply modifications as you see fit, compile it and test it on your camera.

Don't be afraid to change anything! From a safety point of view you can modify any files. There is no code in the sources which allows to update (rewrite) the original firmware (read here). So, the worst thing which can happen is just that the new code wont work. If that happens, turn off the cam or remove the batteries, and everything should be fine again.

trunk - This is where the latest CHDK development version is built from. It likely contains code that is unstable and not well tested. It is NOT the source for the stable versions available from the CHDK autobuild server.

loader - Initial code ran by camera. Sets up various things. No need to modify anything here (except perhaps if you want to port the CHDK onto a new camera model).

platform - Camera-/Firmware-dependent code. You only need to modify anything here if you want to add new references to functions of the original firmware.

platform/generic - Camera-/Firmware-independent code. You only need to modify anything here if you want to add new references to functions of the original firmware.

script - Example scripts. Not needed for compiling your own version.

tools - Tools to make life easier :). You only need to modify anything here if you want to add new references to functions of the original firmware.

branches - Branches are used for both stable version(s) of the CHDK tree and for special development versions.

release-1_0 - the stable branch as of Dec 26, 2011. This branch holds the latest stable release available from the CHDK autobuild server. The only changes made to this branch are bug fixes and the addition of new cameras as they are ports.

There are also a few older branches in there worth mentioning. Note that all of these branches are abandoned and discontinued now.

dataghost - DataGhost's experimental branch with LOTS of nice things he found out (mainly about the s5is) - see here

grand - grAnds original branch

juciphox - a quite new branch created by Jucifer and PhyrePhoX which then later was merged into the main CHDK

old-trunk - well, the old trunk - before the merging of JuciPhoX

vitalyb - backup of the original branch by the founder of CHDK - vitalyb